A magnetic head/disk tester is an instrument that is used for testing the characteristics of magnetic read/write heads and disks for various performance parameters, such as a signal-to-noise ratio, track profile, etc. A magnetic head/disk tester is operable to simulate motions of a head with respect to a disk that occur in an actual hard disk drive during operation. A tester comprises a mechanical component, commonly referred to as a spinstand, that performs movements of the head with respect to the disk, and an electronic component that is responsible for measurement, calculation, and analysis, of signals measured in response to applied test signals.
Examples of prior art spinstands for a head and disk tester, include the Guzik V2002 X-Y Positioning Spinstand and the Guzik 5-1701B Micro-Positioning Spinstand, both of which are available from the assignee of the present disclosure, Guzik Technical Enterprises, 2443 Wyandotte Street, Mountain View, Calif. 94043, USA (www.guzik.com).
When testing a head, or a disk, with a spinstand, it is usual practice to perform the testing with a magnetic read/write head included as a part of a head gimbal assembly (HGA). An example of a conventional HGA 100 is shown in FIG. 1. The basic components of HGA 100 are a head 102, a load beam 104, a flat-bottomed base plate 108 having a boss hole 110 with an angled (with respect to the bottom of base plate 108) peripheral surface 110a, a flex circuit 112, flex circuit (connector) pads 118, and shunt tab 114. The angled surface 110a of the boss hole 110 is used for clamping the HGA 100 to a mounting surface of the spinstand. The flex circuit 112 includes electrically conductive paths for coupling the head 102 by way of flex circuit (connector) pads 118 to external head test circuitry, including a head amplifier (not shown).
During testing, it is important that a head is positioned with great accuracy relative to a disk on a tester. It is also important that the positioning of successively tested heads is consistently repeatable. These requirements are generally met by incorporating in the tester, a clamping mechanism that couples a head gimbal assembly (HGA) and the spinstand, ensuring highly accurate positioning of the HGA.
In the prior art, the clamping mechanism of a spinstand is typically realized as a so-called “collet assembly”, for example, as shown and described in U.S. Pat. No. 7,529,635, U.S. Pat. No. 7,542,868, US Patent Application Publication No. 2008/0062564, and others. A diagram of such a collet assembly 200 is shown in FIG. 2. The collet assembly 200 includes an integrated air piston disposed within a cylindrical interior region defined by housing 214 of the collet assembly 200. The cylindrical interior region extends along and about a vertical (as shown in FIG. 2) axis V.
The air piston comprises a piston top 208, a retainer 210 and an O-ring 206, all moveable together along the vertical axis during testing, inside the collet housing 214. A flat top surface of the housing 214, extending transverse to the vertical axis, is the mounting surface 224 against which the flat underside of base plate 108 of HGA 100 is placed for testing of the head of the HGA.
A set of four sealing O-rings 222 is also disposed within the housing 214 of collet assembly 200. An uppermost of O-rings 222 is disposed about an uppermost portion of the piston top 108, forming a sliding pneumatic seal between that portion and an inward facing surface of the cylindrical interior of housing 214. A next lower of O-rings 222 is disposed about a junction of piston top 208 and retainer 210. That next lower of O-rings 222 pneumatically isolates an upper region 220 of the cylindrical interior region above the top 208 of the air piston, from a lower region 218 below the retainer 210, while permitting vertical sliding motion of the air piston with respect to housing 214.
The collet assembly 200 further comprises a set of four elongated collet fingers 204 (two of which are shown in FIG. 2) extending in part in the direction of the vertical axis. The collet fingers 204 are angularly dispersed about the vertical axis in a uniform manner. The collet fingers 204 include inward facing (i) lower straight edge surfaces extending in the direction of elongation, (ii) cam surfaces extending therefrom (inward with respect to the vertical axis) at an offset angle, and (iii) upper straight edge surfaces extending in the direction of elongation. The collet fingers 204 further include outwardly, radially extending clamp ends 204A at their distal (uppermost as shown in FIG. 2) ends. The distal ends of the collet fingers 204 (as shown in FIG. 2) extend through an aperture of piston top 208 with the air piston in its uppermost position along axis V.
The inner facing lower surfaces of the collet fingers 204 facing the vertical axis, are disposed about a cylindrical outer surface of a spreader pin 212 extending along the vertical axis from a spreader base 216. The spreader pin 212 has a conical surface at its uppermost end. The spreader pin 212 is stationary in the direction of axis V throughout operation, with its lowermost end attached to the spreader pin base 216 which is rigidly coupled to housing 214. The angled cam surfaces of fingers 204 are disposed adjacent to the conical end surface of pin 212, in the position of the piston shown in FIG. 2.
The lowermost two O-rings of the set 222 are disposed about spreader base 216, and respectively effect a pneumatically sealing junction between spreader pin base 216 and an inward facing surface of retainer 210, and between spreader base 216 and an inward facing surface of the cylindrical interior region of the housing 214.
The O-ring 206 fits around a lowermost portion, or base end, of the fingers 204 and provides a radially inward (with respect to the vertical axis) force to resiliently bias the fingers 204 radially inward.
Prior to mounting an HGA 100 for test, pressurized air is applied to region 218 via a port P1 (not shown), which drives piston top 208 upward along the vertical axis, to the position shown in FIG. 2. In that initial position, the inner facing lower surfaces of collet fingers 204 of collet assembly 200 are biased against the cylindrical outer surface of spreader pin 212 with the distal ends of fingers 204 extending maximally above mounting surface 224. Radially extending lips at the upper end of retainer 210 hold the fingers 204 in place relative to the piston top 208. In this position, as illustrated in FIG. 2, the distance spanning the clamp ends 204A at the distal ends of the fingers 204 is less than the diameter of the boss hole of an HGA 100 to be tested.
With collet assembly 200 in the initial position of FIG. 2, in order to mount an HGA 100 to surface 224 of collet assembly 200, HGA 100 is lowered with its boss hole 110a slipping over the distal ends of the extended fingers 204 so that the flat-bottomed base plate 108 rests on surface 224. In their maximally extended (in the direction of the vertical axis as shown in FIG. 2) initial position, the inward facing lower surfaces of fingers 204 are biased by O-ring 206 against the cylindrical outer surface of spread pin 212.
Then, in response to pressurized air (with pressure greater than the pressure in lower region 218) introduced to upper region 220 via a port P2 (not shown), the piston top and retainer 210, as well as fingers 204, are driven downward along the vertical axis. As the fingers 204 move downward, the inward angled cam surfaces of the fingers 204 engage the conical surface at the tip of spreader pin 212, causing an outward directed force on the fingers 204, overcoming the bias applied by O-ring 206 and spreading the distal ends of fingers 204 so that the distal ends of fingers 204 span a distance greater than the innermost diameter of the angled edge 110a of boss hole 110 in the base plate 108 of the HGA adjacent to surface 224, and through continued downward motion, the downward facing surfaces of the radially extending clamp ends of pins 204 ultimately engage surface 110a surrounding boss hole 110 of base plate 108 of HGA 100, thereby clamping HGA 100 to surface 224.
To release a clamped HGA 100, pressurized air (at a pressure greater than that in upper region 220) is introduced to lower region 218, causing upward movement of the piston top 208, retainer 210 and fingers 204, and the distal ends of the fingers return to the initial state with the distal ends of fingers 204 maximally separated from surface 224 in the direction of the vertical axis, and inwardly biased with the lower surfaces of fingers 204 again biased by O-ring 206 against the outer cylindrical surface of spreader pin 212, thereby releasing HGA 100.
While the above-described collet assemblies of the prior art, do allow testing of head and disks in some form, there is much room for improvement in many factors in order to meet developing demand for improved heads and reasonable prices for today's market.
For example, in order to optimize operation in one sense, a collet assembly for a head and disk tester should be lightweight to make possible fast movement of the HGA during positioning of the head over the disk. On the other hand, the housing must have a rigid mounting area to support the HGA, in order to be able to attain high accuracy testing for a unit, and enabling repeating of such tests over large numbers of production units. To partially address these requirements in prior art collet assemblies for head and disk testers, such as that shown in FIG. 2, the housings are typically made from titanium, which is lightweight as well as strong. However, titanium is a costly material that raises the cost of prior art collet assemblies for head and disk testers as a whole.
More importantly, in prior art collet assemblies such as that shown in FIG. 2, the clamping forces which the various collet fingers apply to the angled surface 110a of a boss hole 110 of an HGA, typically vary significantly from one finger to another. The difference in the clamping forces applied by the different fingers, leads to a skewing of the base plate 108 of the HGA 100 relative to the mounting surface 224. Such a skewing disrupts correct positioning of the HGA, affects the accuracy and the repeatability of tester measurements, and can cause damage to the disk.
Also, as seen in the typical prior art collet assembly of FIG. 2, the lower end of the spreader pin 212 is rigidly secured in the spreader base 216, while the upper end spreader pin 212 is not rigidly fastened to the housing, allowing the distal (or top as shown) end of the spreader pin 212 to be unrestrained with respect to movement in a radial direction. As a consequence, during movements of the air piston in such prior art collet assemblies, the unsecured end portion of the spreader pin bends during the movements of mounting an HGA. Such bending results in radially directed movement of the upper end of the spreader pin, causing unwanted displacement of an HGA base plate to occur during placement into its test position on the tester. A direct consequence of such a misplacement of an HGA, is test results which do not accurately reflect the true characteristics of the head of the HGA.
Moreover, with passage of time, the elasticity of the O-ring which effects inward bias to the fingers, tends to diminish, resulting in a corresponding reduction in the retracting force that keeps the fingers 204 together prior to their spreading for clamping an HGA. Thus, this diminishment of elasticity is one more factor leading to improper placement of an HGA for testing. As marketplace demands require higher and higher memory storage densities, there arise corresponding requirements for increased accuracy in positioning an HGA for testing in modern head and disk testers, for each head tested and for repeatability of such tests in large scale production.
The above-mentioned disadvantages of known so-called collet assemblies for head and disk testers raise the cost for testing, and in some cases prevent the needed accuracy and reliability of testers. The disclosure set forth below, provides improvements in the design and construction of prior art so-called collet assemblies (while referring to the improved assemblies as “mounting apparatuses”) for head and disk testers. The mounting apparatuses of the disclosure substantially reduce, and in most cases fully eliminate, the above-noted deficiencies of prior art so-called collet assemblies of, or for, head and disk testers, while also reducing the cost compared to prior art collet assemblies, and testers for which they are a part, and at the same time, improving the performance, of such testers with the improved mounting apparatuses.